1. Field of the Invention
The present invention relates to a method for manufacturing mirror surface tubes for a photosensitive drum of a copying machine or the like.
2. Description of Related Art
Recently, demand for office automation (OA) machines, such as a copying machine, a printer or the like, is increasing for improvement of efficiency of office jobs, and demand for lighter weight and higher quality images for such machines is also increasing. Conventionally, a mirror surface tube made of aluminium or aluminium alloy is used for a photosensitive drum of a copying machine, a printer or the like. The surface of the mirror tube is coated with an organic photosensitive compound (OPC), amorphous silicon (Si), selen (Se) or other material. In this case, the mirror surface tube, that is a substrate of the photosensitive drum is required to have a very small surface roughness, good smoothness and no surface defect such as scratches.
An extrusion or pultrusion aluminium or aluminium alloy tube has a lot of surface defects and unevenness, which should be removed in order to obtain a desired surface roughness by the mirror process, e.g., known as a diamond grinding process, centerless grinding process, burnishing process or electrolytic integrated polishing process.
However, the above-mentioned processes have a lot of problems. The diamond grinding process is expensive, low in productivity and yield drop. This process also easily generates surface defects such as plucking or sticking abrasive grains as well as a bad dimension accuracy such as roundness or bent. Furthermore, the finished mirror surface by this process easily generates an interference band due to reflection characteristics, which may cause a stripe pattern on a printed surface.
The centerless grinding process possibly generates a local scratch due to grind grains dropped from a grindstone. It is difficult to remove this scratch later by a burnishing process.
The burnishing process possibly generates a surface defect involving a crease or plucking when pulling out a raw tube. Therefore, a photosensitive drum using this tube may cause a print defect.
The electrolytic integrated polishing process may generate a lot of surface flaws, such as plucking or sticking, as well as a bad dimensional accuracy, such as roundness or bending since electrodes that perform electrolysis action and grinding material that performs grinding action work independently of each other, and an arrangement of the grinding material is uneven relative to the raw tube. Especially, it is difficult to apply this process to an external surface of an aluminium or aluminium alloy tube.
In the above-mentioned techniques, it is difficult to ensure a quality required for a mirror surface tube used for a photosensitive drum because aluminium material is so soft that surface flaws, such as plucking or sticking, can be generated easily due to grinding material or grinding action.
A mirror surface tube for a photosensitive drum is required to have a finished surface with a high accuracy, which is coated with a thin OPC film, as mentioned above, uniformly for high sensitivity. Furthermore, smoothness of the surface is an important characteristic required for the mirror surface tube, since a minute recess on the surface of the mirror surface tube can be a reservoir of toner, which is required to have micro particles for obtaining a micro dot of high quality image.
The object of the present invention is to solve the above-mentioned problems of the prior art and to provide a method for manufacturing a mirror surface tube for a photosensitive drum of a copying machine or the like, by which an external surface of an aluminium or aluminium alloy tube can be mirror-processed with high accuracy without surface defects utilising advantages of a centerless grinding process, electrolytic integrated polishing process and burnishing process. The method should ensure good quality required for a photosensitive drum and should improve dimension accuracy such as roundness and yield in production.
In order to attain the above-mentioned object, a method according to the present invention comprises the steps of preparing a long sized aluminium or aluminium alloy tube finished in predetermined shape and dimension with a surface roughness of 10 microns or less, performing a centerless grinding process on the tube, cutting the centerless-ground tube into a predetermined length, and polishing the cut tube by an electrolytic integrated polishing apparatus including a tool electrode mechanism having a special elastic grindstone including a tool electrode mechanism having a special elastic grindstone to obtain an external surface with a surface roughness of 2.0 microns or less.
According to another aspect, the method comprises the steps of preparing a long sized aluminium or aluminium alloy tube finished in predetermined shape and dimension with surface roughness of 10 microns or less, cutting the tube into a predetermined length, performing centerless grinding process of the cut tube, and polishing the centerless-ground tube by an electrolytic integrated polishing apparatus for an external surface of a cylinder including a tool electrode mechanism having a special elastic grindstone so as to finish the surface roughness of 2.0 microns or less.
Preferably, the aluminium or aluminium alloy tube finished by the above-mentioned method into the surface roughness of 2.0 microns or less is further processed by a roller burnishing process using a plurality of burnishing rollers arranged on a circle so as to finish the surface roughness to 0.5 microns or less.
According to still another aspect, the method comprises the steps of preparing an aluminium or aluminium alloy tube having a surface roughness of 10 microns or less, performing a centerless grinding process on the tube, performing electrolytic integrated polishing process of the centerless-ground tube so as to finish the surface to a roughness of 0.5 microns or less, and performing a roller burnishing process on the electrolytic polished tube so as to finish the surface roughness to 0.1 microns or less.
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.